(1) Field of the Invention
This invention relates to the use of vegetable oil adducts, either alone or in combination with vegetable oils and/or modified vegetable oils as additives in skin and hair care products. More particularly, this invention relates to the use of both water-soluble and water-insoluble salts of vegetable oil adducts with or without vegetable oils or modified vegetable oils as emollients in skin and hair care products. Specifically, this invention relates to the use of adducts prepared from vegetable oils containing nonconjugated polyunsaturated fatty acid esters which are conjugated and then modified via Diels-Alder addition with acrylic acid, fumaric acid or maleic anhydride as emollients in skin and hair care products.
(2) Description of the Prior Art
Skin is made up of several layers of cells which coat and protect the keratin and collagen fibrous proteins that form the skeleton of its structure. The outermost of these layers, known as the stratum corneum, is known to be composed of 250 .ANG. protein bundles surrounded by 80 .ANG. thick lipid layers. Anionic surfactants typically penetrate the stratum corneum membrane and, by delipidization (i.e., removal of the lipids from the stratum corneum), destroy its integrity. This destruction of the skin surface topography leads to a rough feel and may eventually permit the surfactant to interact with the keratin, creating irritation.
Organic solvents are a major cause of delipidization of the stratum corneum. Also, solvents or solvent mixtures which are both lipid soluble and water soluble are most effective in delipidization, sometimes removing as much as 10% to 20% of lipids from the skin upon long soaking. Specific chain length ranges of less water soluble organics are also deleterious. Hydrocarbons of the chain lengths present in kerosene (boiling range 272.degree. C. to 333.degree. C.) interact with the lipids to produce abnormal thickening of the stratum corneum. Kerosene, of course, is a common component utilized in waterless hand cleaners. Medium chain length surfactants such as sodium lauryl sulfate and .alpha.-olefin sulfonates commonly used in dish washing detergents are deleterious to the skin even in very dilute solutions. The activity of this class of substances is thought to be due to a strong binding of the surfactant functional group with protein molecules in the keratin filaments causing them to be reversibly denatured from the .alpha.-helix to the .beta.-configuration through an uncoiling of the filaments which expands the tissue. Once this has occurred, complete recovery of the barrier function probably does not occur even after all of the surfactant is removed because of the complex composition and nature of the stratum corneum.
Cosmetic creams which employ mineral oil also include vegetable oils for partial replacement of skin surface lipids removed due to the solvent action of the mineral oil. However, only relatively recently has it been recognized that the moisture content of the skin is equally important.
The proper water gradient across the stratum corneum is important to its functionality. Most of this water, which is sometimes considered to be the stratum corneum's plasticizer, comes from inside the body. If the humidity is too low, such as in a cold climate, insufficient water remains in the outer layers of the stratum corneum to properly plasticize the tissue; and the skin begins to scale and becomes itchy. Skin permeability is also decreased somewhat when there is inadequate water across the stratum corneum. On the other hand, too much water on the outside of the skin causes the stratum corneum to ultimately sorb three to five times its own weight of bound water. This swells and puckers the skin and results in approximately a two to three fold increase of the permeability to water and other polar molecules above the permeability at optimum hydration.
Hair consists of many of the same constituents as the stratum corneum. The outermost region of cells forms a rather thick chemically resistant protective coating enclosing the hair fiber which is called the cuticle. The surface of the cuticle is covered with a thin layer called the epicuticle which is thought to contain lipids and protein. The cuticle envelopes the cortex cells which comprise the major part of the fiber mass. Keratinization takes place in the cortex to build stability into the hair structure.
Thus, a need exists for substances which will assist the stratum corneum and hair cuticle in maintaining their barrier and water retention functions at optimum performance in spite of deleterious interactions which the skin and hair may encounter in washing, work, and recreation.
In the discussion on cosmetic creams and lotions in the Encyclopedia of Chemical Technology, Third Edition, Volume 7, a classic example of a cream formulation is given which includes 11.8-12.1% spermaceti. It is also noted that modern formulations which employ mineral oil in place of the earlier used almond oil must include vegetable oil for partial replacement of skin surface lipids removed by the solvent action of the mineral oil.
Cosmetic lotion formulations are almost identical to the creams except an oil-in-water emollient lotion usually contains more water than the corresponding cream. These lotions are preferred for use during the day because they produce a lighter or less oily emollient film. Cosmetic lotion formulations in the Encyclopedia of Chemical Technology include 1-1.5% lanolin anhydrous as the primary emollient.
Unfortunately, emollient additives presently employed in creams and lotions do not provide the persistency desired in their skin softening effects. Therefore, a particular need exists for emollient additives which promote skin softening for a longer period of time than presently available emollients.
Hair preparations also may benefit from inclusion of emollients. The barrier and water retention functions of the hair cuticle may be assisted similarly to the stratum corneum of the skin, particularly in shampoos and hair straighteners. Lanolin and its derivatives are included in shampoo formulations as conditioning agents to impart ease of combing, detangling, body, shine, manageability, split-end mending, and prevention of static build-up.
The beneficial effects of emolliency to both skin and hair may be appreciated most in dandruff shampoos. Dandruff is the product of hyperkeratinization. The rate of keratinization increases to the point that the scales become more visible. Dandruff shampoos contain ingredients that effectively control dandruff by allowing a normal turnover rate of epidermal cells. A skin and hair softening emollient should reduce the rate of keratinization in the scalp stratum corneum and, at the same time, benefit the hair cuticle.
Therefore, an object of the present invention is to provide additives for skin and hair preparations. A further object is to provide skin and hair preparation emmollient additives which give a softening effect to the skin stratum corneum or the hair cuticle. A still further object of this invention is to provide skin and hair preparation additives which provide a more persistent softening effect than known emollients.